Anaerobic lagoon or tank design for eflluent carbon to nitrogen ratio control

ABSTRACT

An anaerobic lagoon wastewater treatment system, which includes a plurality of wastewater treatment zones. The treatment zones are either formed by providing a plurality of separate lagoons or by providing one or more partitioning elements within one lagoon. One or more treatment zones may also be provided in the form of a tank. The first wastewater treatment zone in the direction of wastewater flow has a smaller volume than the second wastewater treatment zone. Further, the first wastewater treatment zone achieves a significant reduction in fat, oil and grease removal, as well as in total suspended solids removal, but only a modest reduction in biological oxygen demand. An effluent from the first wastewater treatment zone is mixed with an effluent from the second wastewater treatment zone such that a predetermined ratio of carbon to nitrogen is maintained within the mixture of first and second effluents.

FIELD OF THE DISCLOSURE

An anaerobic lagoon biological wastewater treatment system is providedthat allows to control the carbon to nitrogen ratio, or biologicaloxygen demand (BOD) to total Kjeldahl nitrogen (TKN) ratio, of thewastewater treated by and discharged from the wastewater treatmentsystem.

BACKGROUND

Anaerobic Lagoons (ALs) are typically earthen basins filled withwastewater, which undergoes anaerobic respiration as part of a systemdesigned to manage and treat wastewater from poultry slaughter houses.Once in the lagoon, wastewater undergoes, among other reactions, theprocess of anaerobic respiration, whereby volatile organic compounds areconverted into carbon dioxide and methane. ALs are typically operated ona five day per week schedule, with little or no production of wastewaterover weekends and on holidays.

Anaerobic Lagoons are designed to provide BOD, Total Suspended Solids(TSS), and Fat, Oil and Grease (FOG) removal. The anaerobic biologicaltreatment process typically provides approximately 70% to 90% BODremoval, 80% to 90% FOG removal, and reduces TSS concentrations down to100 to 300 mg/L. By contrast, the AL process provides only minimal TKNand Total Phosphorous (TP) nutrient removal of about 5% to 15%.Consequently, a typical AL design providing 80% BOD and 10% TKN removalresults in AL effluent with a BOD/TKN ratio below 1. However, a BOD/TKNof 3.0 or higher is normally required to achieve efficient nitratenitrogen removal by biological denitrification in a downstream activatedsludge treatment process. Accordingly, existing AL technology isproblematic in that ALs remove most of the BOD to generate biogas butremove very little nitrogen causing the typically very low AL effluentBOD/TKN ratio.

More recent AL designs have used influent short circuiting or partial ALbypassing to attempt to raise the AL effluent BOD concentration andBOD/TKN ratio of the AL effluent wastewater or the downstream processblend effluent wastewater. Influent short circuiting is accomplished byuse of an alternate AL influent pipeline, which can discharge acontrolled portion of the total influent flow volume into the outlet endof the AL in order to allow for FOG and TSS removal from the shortcircuited portion of the wastewater while significantly reducing theremoval of soluble and colloidal BOD from the short circuitedwastewater. Influent short circuiting produces a treated wastewaterblend that has a higher BOD concentration, and, therefore, a higherBOD/TKN ratio in order to provide an adequate BOD carbon source forefficient biological denitrification in a downstream activated sludgetreatment process.

The short circuit design or the partial bypass design, however, are notalways effective, especially on weekends or holidays when a processingplant is typically not in operation, and, therefore there is nowastewater to short-circuit to the outlet end of the AL or to bypass theAL. Consequently, even when the short circuit AL lagoon design or ALlagoon bypass design is used, the blended AL effluent wastewater BOD issignificantly decreased on weekends and holidays, when there is noinfluent wastewater flow because the processing plant is not inoperation.

SUMMARY OF THE DISCLOSURE

Disclosed herein is a biological wastewater treatment system comprisingan anaerobic lagoon and/or a tank with a plurality of wastewatertreatment zones.

In one aspect of the disclosure, an anaerobic lagoon wastewatertreatment system is provided that comprises an anaerobic lagoon or atank, a partitioning element positioned within the anaerobic lagoon orthe tank to define a plurality of wastewater treatment zones, and afirst effluent pipeline for transporting an effluent from a firstwastewater treatment zone from among the plurality of wastewatertreatment zones to an outlet end of the anaerobic lagoon or an outletend of the tank.

In another aspect of the disclosure, an anaerobic lagoon wastewatertreatment system is provided that comprises a plurality of anaerobiclagoons, a first pipeline for connecting a first anaerobic lagoon to afinal anaerobic lagoon from among the plurality of anaerobic lagoons,and a second pipeline to transporting an effluent from the firstanaerobic lagoon to an outlet end of the final anaerobic lagoon.

In yet another aspect of the disclosure, a method of controlling aneffluent carbon to nitrogen ratio of an anaerobic lagoon is provided,which comprises providing an anaerobic lagoon, a tank or an anaerobiclagoon and/or a tank having a plurality of wastewater treatment zones;reducing an initial biological oxygen demand (BOD) concentration to afirst BOD concentration in the first wastewater treatment zone fromamong the plurality of wastewater treatment zones; reducing the firstBOD concentration to a second BOD concentration in a final wastewatertreatment zone from among the plurality of wastewater treatment zones;wherein a difference in concentration between the initial BODconcentration and the first BOD concentration is smaller than thedifference in concentration between the first BOD concentration and thesecond BOD concentration; and mixing a first effluent from the firstwastewater treatment zone with a second effluent from the finalwastewater treatment zone and/or conducting the first effluent into thefinal wastewater treatment zone, or conducting the first effluentdirectly to a downstream activated sludge denitrification reactor in anitrification-denitrification biological nitrogen and phosphorousremoval system.

Further, the disclosed anaerobic lagoon systems provide for one or moreinfluent zone cells or effluent zone cells in which only a lowpercentage of BOD removal occurs in the wastewater. Wastewater can bepumped or discharged at a controlled flow rate and volume from one ofthese “high BOD” cells to mix with wastewater pumped or discharged fromthe effluent or outlet end of the AL to produce a blended total effluentflow volume with higher BOD/TKN ratio. This AL design provides for muchmore accurate control of AL BOD/TKN ratio over the entire 7 day/weektime period because the BOD concentration in the effluent zone or “highBOD” cell will drop or be reduced much less than in the outlet zone ofthe AL over weekends or holidays, thereby allowing the blended final ALeffluent to maintain a higher BOD concentration and BOD/TKN ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawingswherein:

FIG. 1 depicts a plan view of anaerobic lagoon 100, which includes twopartitioning elements 120 and 120′. The two partitioning elements 120and 120′ divide the interior space of the anaerobic lagoon into threewastewater treatment zones 110, 110′, and 110″.

FIG. 2 depicts anaerobic lagoons 200 and 210, whereby anaerobic lagoon200 is provided upstream of anaerobic lagoon 200. Further, anaerobiclagoon 210 is smaller than anaerobic lagoon 200, i.e., has a smallervolume for receiving and storing wastewater.

FIG. 3 depicts an anaerobic lagoon 300 from the related art, whichincludes short-circuit line 350 and bypass line 330.

FIG. 4 depicts a section view of anaerobic lagoon 400, which includesgas containment and collection cover 430.

FIG. 5 depicts related art anaerobic lagoon 500, which includes gascontainment and collection cover 510.

FIG. 6 depicts a section view of a wastewater treatment system in whichthe wastewater treatment zones are provided by installing partitions 610and 610′ within tank 600.

FIG. 7 depicts a plan view of the wastewater treatment tank 600 in whichan effluent can be directly withdrawn from the high BOD cells throughbypass lines 720 or 720′.

DESCRIPTION OF THE BEST AND VARIOUS EMBODIMENTS

The foregoing and other objects, aspects, and advantages will be betterunderstood from the following detailed description of the best andvarious embodiments. Throughout the various views and illustrativeembodiments of the present disclosure, like reference numbers are usedto designate like elements.

The anaerobic lagoon biological wastewater treatment system disclosedherein comprises a plurality of wastewater treatment zones, i.e., two ormore wastewater treatment zones. In a preferred embodiment, theplurality of wastewater treatment zones are provided as partitions of acommon anaerobic lagoon, which are formed by one or more partitioningelements located within the lagoon. In another preferred embodiment, theplurality of wastewater treatment zones corresponds to a plurality ofanaerobic lagoons, which are connected in series. In a furtherembodiment, two or more wastewater treatment zones are provided aspartitions of a tank.

The first wastewater treatment zone is provided as a wastewater influentzone and receives the wastewater to be treated. In a typical embodiment,wastewater enters the first wastewater treatment zone through awastewater intake port and an effluent exits a final wastewatertreatment zone through an anaerobic lagoon outlet.

With particularity, the first wastewater treatment zone has a smallervolume than the final wastewater treatment zone. Also withparticularity, the partitioning element has a plurality of flow holes ina vicinity of a lagoon bottom, which allows wastewater to flow from awastewater treatment zone into an adjacent wastewater treatment zone,such that a liquid level is substantially the same on both sides of thepartitioning element.

In a typical embodiment, the anaerobic lagoon wastewater treatmentsystem further comprises a biogas containment cover. In another typicalembodiment, the anaerobic lagoon further comprises a biogas collectionsystem.

In a particular embodiment, the anaerobic lagoon comprises onepartitioning element to define the first wastewater treatment zone andthe final wastewater treatment zone. In another particular embodiment,the anaerobic lagoon comprises two partitioning elements to define thefirst wastewater treatment zone, a second wastewater treatment zone, andthe final wastewater treatment zone.

Typically, the plurality of anaerobic lagoons further comprises a secondeffluent pipeline for transporting an effluent from the secondwastewater treatment zone to the outlet end of the anaerobic lagoon.

Also typically, the partitioning element is selected from the groupconsisting of a concrete wall, a floating, optionally movable,cable-mounted membrane, and a fixed cable-mounted membrane.

In a particular embodiment, the partition is movable to allow foradjusting of the volume of an adjacent wastewater treatment zone.Specifically, if only the first partition is moved towards thewastewater inlet, the volume of the first wastewater treatment zone isreduced while the volume of the second or final wastewater treatmentzone is increased. Accordingly, the volume of the second wastewatertreatment zone may be adjusted by moving the first and/or the secondpartition.

With particularity, the plurality of anaerobic lagoons comprises abiogas containment cover. Typically, each lagoon comprises a separatebiogas containment cover, which may be provided as a single containmentcover covering the entire lagoon. Also typically, the plurality oflagoons comprises a biogas collection system.

In a typical embodiment, the amount of the first effluent is adjusted tomaintain a predetermined ratio of effluent carbon to nitrogen and/oreffluent carbon to phosphorous downstream. In another typicalembodiment, a first wastewater detention time and volume are selectedfor the first wastewater treatment zone and a final wastewater detentiontime and volume are selected for the final wastewater treatment zone,wherein the final wastewater detention time is about four to ten timeslonger than the first wastewater detention time.

With particularity, for example, the first wastewater detention time isof from about twelve hours to about two days, more particularly aboutone day, and the final wastewater detention time is of from about twodays to about twenty days, more particularly about ten days.

In a particular embodiment, the BOD concentration of the wastewater inthe first wastewater treatment zone is reduced by about 20% to 30%. Inanother particular embodiment, a first volume of the first wastewatertreatment zone is of from about 10 to 20% of a total volume of theplurality of wastewater treatment zones and a second volume of thesecond wastewater treatment zone is of from about 10 to 20% of a totalvolume of the plurality of wastewater treatment zones. In a furtherparticular embodiment, the predetermined ratio of effluent carbon tonitrogen is at least 4:1. In yet another particular embodiment, theratio of effluent carbon to phosphorus is at least 20:1.

Turning to the drawings, FIG. 1 shows a preferred embodiment of ananaerobic lagoon 100 provided with partitioning elements 120 and 120′,which divide the lagoon interior into three wastewater treatment zones,in particular into first wastewater treatment zone 110, secondwastewater treatment zone 110′, and final wastewater treatment zone110″. It is within the scope of this disclosure to provide at least onepartitioning element to partition a lagoon into two wastewater treatmentzones, but there is no particular limit on the number of partitioningelements that may be provided and, thus, on the number of partitionscreated.

The multiple wastewater treatment zones or cell partitions are designedto provide segregation of AL zones. The partitioning elements orpartitions have flow holes near the lagoon bottom to allow wastewater topass from one zone into the next zone. The partitions therefore are notnormally designed structurally to retain hydraulic pressure or to allowthe side of the partition to be drained while the other side is full ornot drained. The partitioning elements preferably are a floatingcable-mounted membrane or an attached cable-mounted membrane. However,this disclosure is not limited to the above listed materials for apartitioning element. Rather, any structure capable of partitioning thelagoon interior may be used.

In one aspect of the disclosure, an existing anaerobic lagoon isconverted into an anaerobic lagoon capable of maintaining an effluentcarbon to nitrogen ratio by installing a partition element within theexisting lagoon, such as by installing a fixed, cable-mounted membranepartition. In another aspect of the disclosure, an existing tank isconverted by providing a partition, such as a floating cable-mountedmembrane, inside of the tank. It is further possible to adjust therespective volumes of the wastewater treatment zones created by theinstallation of the partition or partitions by providing movablepartitions, such as a movable floating cable-mounted membrane.

Wastewater that has been partially treated flows from the firstwastewater treatment zone 110 through the flow holes near the bottom ofpartitioning element 120 into the second wastewater treatment zone 110′.After further treatment, wastewater flows into the final wastewatertreatment zone 110″.

Wastewater enters the first wastewater treatment zone of lagoon 100through wastewater intake port 160. The first and second wastewatertreatment zones 110 and 110′ are operated as high BOD cells, i.e.,wastewater treatment zone containing wastewater having a high BODconcentration, by shortening the detention time of wastewater thereincompared to the detention time typically used for wastewater in a lagoonof the size of the entire lagoon 100. The shorter detention timeprevents the markedly reduction in BOD concentration that is achievablein an undivided lagoon undergoing prolonged anaerobic treatment. One ormore high BOD cells can be used.

Typically, 50% to 80% TSS and Oil and Grease removal occurs in the highBOD cells, while a much lower BOD removal yield of approximately 20% to30% occurs due to the reduced volume and detention time in the High BODcell(s). Partially treated wastewater can be pumped out of wastewatertreatment zones 110 and 110′ through effluent lines 171 and 171′,respectively, using pump 130. The effluent flow rate is measured withflow meter 140. Further, the effluent line includes valve 150.

The high BOD effluent from either or both of wastewater treatment zones110 and 110′ is mixed downstream of the final wastewater treatment zone110″ with a low BOD effluent obtained from the final wastewatertreatment zone 110″ through effluent line 170. The mixture of low andhigh BOD is transported for further treatment as mixture effluent 180.

Providing two wastewater treatment zones as high BOD cells allows tomore accurately adjust the BOD/nitrogen ratio and BOD/phosphorous ratiodownstream of the final wastewater treatment zone.

FIG. 2 shows another preferred embodiment of an anaerobic lagoon havinga plurality of wastewater treatment zones. In this case, the separatewastewater treatment zones are not provided as partitions of a commonlagoon, but as separate lagoons connected by wastewater-carrying lines,such as pipelines or troughs. Specifically, anaerobic lagoon 210 isprovided upstream of anaerobic lagoon 200 and is operated as a firstwastewater treatment zone, i.e., as a high BOD cell. Wastewater to betreated enters anaerobic lagoon 210 through influent port 220 andundergoes anaerobic treatment.

The volume of anaerobic lagoon 210 is smaller than the volume ofanaerobic lagoon 220, which results in a shorter average detention timefor wastewater in anaerobic lagoon 210. Consequently, only about 20 to30% BOD removal occurs in the first anaerobic lagoon. Partially treatedwastewater leaves anaerobic lagoon 210 as effluent 230 and is conductedinto anaerobic lagoon 200, which is operated as a final wastewatertreatment zone. Anaerobic lagoon 200 has a larger volume and, therefore,a longer average wastewater detention time and higher BOD removal yieldto achieve a low BOD concentration. After anaerobic treatment,wastewater leaves anaerobic lagoon 200 as effluent 250 and is mixed witheffluent 240, which is obtained from anaerobic lagoon 210 directly. Themixture of effluent 240 and effluent 250 is conducted to a furtherwastewater treatment process as partially treated wastewater 260.

More than one anaerobic lagoon 210 may be provided upstream of anaerobiclagoon 200. If more than one anaerobic lagoon 210 is provided, theanaerobic lagoons are connected in series and each anaerobic lagooncomprises an effluent line for mixing an effluent downstream of theanaerobic lagoon 200. However, due to space restrictions at the site ofthe wastewater treatment facility, typically only one anaerobic lagoon210 is provided.

It is one aspect of the disclosure to install a smaller lagoon upstreamof an existing anaerobic lagoon of a wastewater treatment facility toconvert the existing anaerobic lagoon of the facility into an anaerobiclagoon system capable of maintaining an effluent carbon to nitrogenratio.

Further, it is within the scope of this disclosure to provide ananaerobic lagoon system that comprises a plurality of anaerobic lagoonsand a partitioning element. In one preferred embodiment, a smallanaerobic lagoon is provided upstream of a larger anaerobic lagoon,wherein the small anaerobic lagoon additionally contains a partitioningelement. Two effluent lines are provided to transport an effluent fromeach wastewater treatment zone created by the partitioning elementwithin the small anaerobic lagoon.

FIG. 3 shows an anaerobic lagoon of the related art. A wastewater stream320 enters a single anaerobic treatment cell 310 within anaerobic lagoon300. The wastewater stream 320 may be partially diverted through bypassline 330 or short-circuit line 350 and mixed with an effluent fromanaerobic lagoon 300 to obtain partially treated wastewater 340.

FIG. 4 shows a section view of a preferred embodiment of an anaerobiclagoon 400 comprising two partitioning elements 120 and 120′. Thewastewater is retained within the lagoon at a fill level that is locatedof from low water mark 410 and up to high water mark 420. The anaerobiclagoon is covered with a biogas containment cover 430. Biogases, such asmethane, which are produced in the biological anaerobic treatmentprocess, are prevented from escaping the water treatment facility, whichotherwise could constitute a nuisance to neighboring residents.Moreover, the biogases can be collected to either be used as a biofuelon site or sold. The biogases flow through pipe 440 and are compressedby pump 450 to be stored in gas storage tank 460.

FIG. 5 shows an anaerobic lagoon 500 of the related art, which iscovered with a biogas containment cover 510. Wastewater is retainedwithin the lagoon at a fill level which is between low water mark 520and high water mark 530.

Accordingly, the design of anaerobic lagoon 400 provides for biogascontainment, collection, and recycling using a single cover systembecause the partitioning elements do not separate the gas space abovethe lagoon variable liquid level. By contrast, for a plurality ofseparate anaerobic lagoons, each anaerobic lagoon is typically coveredwith a biogas containment cover if biogases are collected and reused asa fuel source. Thus, biogas containment and collection for an anaerobiclagoon design with two separate lagoons and two separate cover systemsis typically more expensive than biogas containment for a singleanaerobic lagoon with partitioning elements, which can be achieved witha single cover system.

FIG. 6 shows a section view of an anaerobic wastewater treatment systemwherein the treatment takes place in a tank 600 instead of an anaerobiclagoon, as discussed above. The tank is provided with two partitions 620and 620′ to create a total of three wastewater treatment zones, inparticular first wastewater treatment zone 610, second wastewatertreatment zone 610′, and final wastewater treatment zone 610″.Wastewater can flow through an opening near the bottom of the partitionsinto an adjacent wastewater treatment zone. Wastewater can be broughtinto the tank up to a maximum fill height 630 leaving a head space abovethe wastewater treatment zones.

Size and shape of the tank 600 are not particularly limited. However, ina preferred embodiment, tank 600 has a cylindrical shape and is madefrom steel. Further, tank 600 is provided as an above gradeinstallation. However, it is also possible to install tank 600 partiallyor fully below grade. Moreover, the tank can be provided having an opentop or as a covered tank.

FIG. 7 depicts a plan view of the wastewater treatment system in FIG. 6.The first two wastewater treatment zones are operated as high BOD cell.From the first and second wastewater treatment zones partially treatedwastewater can be conducted through bypass lines 720 and 720′,respectively, to be mixed with an effluent pumped from the finalwastewater treatment zone 610″ to adjust the effluent carbon to nitrogenand/or carbon to phosphorous ratio.

Further, as depicted in FIG. 7, the volumes of the wastewater treatmentzones are adjustable because the partitions are movable in the directionindicated by arrows 710.

In another preferred embodiment, the anaerobic lagoon is designed andoperated to provide a relatively constant equalized flow. Specifically,the volume of the anaerobic lagoon is sufficient to store wastewaterinflow over a prolonged period, such as 7 days, while the effluentoutput is kept constant. Moreover, if the facility producing wastewateris in operation for less than 7 days per week, for example for 5 daysper week, the equalized flow at the outlet end of the anaerobic lagoonis set to 5/7 times the daily inflow.

The following examples apply to anaerobic lagoon wastewater treatmentsystems having partitioning elements as well as to anaerobic lagoonwastewater treatment systems comprising a plurality of anaerobiclagoons. Specifically, the following examples describe the wastewatertreatment process for an anaerobic lagoon system having a firstwastewater treatment zone and a final wastewater treatment zone, whichmay be provided as separate partitions in a common lagoon or as twoseparate lagoons.

As noted above, the average wastewater detention time in the firstwastewater treatment zone is reduced compared to the detention time inthe final wastewater treatment zone. For example, if the detention timein the final wastewater treatment zone is about 10 days, than thedetention time in the first wastewater treatment zone is selected to beabout 1 day, which provides for good fat, oil, and grease (FOG) removal,but removes less soluble and/or colloidal BOD. Accordingly, the effluentfrom the first wastewater treatment zone has significantly reduced FOGand TSS concentrations, but only a slightly reduced BOD concentration.Further, the effluent from the first wastewater treatment zone has amuch higher ratio of carbonaceous biological oxygen demand (BOD) tonitrogen (BOD/nitrogen ratio or C/N ratio); as well as BOD/phosphorousratio (carbon/phosphorous ratio or C/P ratio) than the final effluentdischarged from the outlet end of the final wastewater treatment zone.

EXAMPLE 1

In the first Example, wastewater having the following initial pollutantconcentrations of 2,000 mg/L BOD, 600 mg/L FOG, 1,500 mg/L TSS, 140 mg/LTKN, and 17 mg/L total phosphorous (TP), which is conducted into a firstwastewater treatment zone, will typically undergo 20 to 30% reduction inBOD concentration. Thus, alongside a 30% BOD reduction to 1,400 mg/L,the other pollutants are reduced to approximately 200 mg/L or less FOG,300 to 400 mg/L TSS, 140 mg/L TKN, and 17 mg/L TP. A certain volume ofwastewater can then be discharged out of the first wastewater treatmentzone and blended with wastewater discharged from the outlet end of thefinal wastewater treatment zone to produce a blended wastewater ormixture with adequately high C/N and C/P ratios for a downstreamactivated sludge treatment process to achieve excellent enhancedbiological phosphorous removal and nitrogen removal bynitrification-denitrification.

A BOD/N (C/N) ratio of at least 4/1 and a BOD/.P (C/P) ratio of at least20/1 are required to achieve high efficiency nitrogen removal bynitrification-denitrification and enhanced biological phosphorousremoval by luxury uptake, respectively. Accordingly, for Example 1having TKN=140 mg/L and TP=17 mg/L, a BOD concentration of 4(140mg/L)+20(17 mg/L)=900 mg/L or more is required to achieve or exceed the4/1 and 20/1 ratios.

COMPARATIVE EXAMPLE

If wastewater having the initial pollutant concentrations of Example 1is treated in an anaerobic lagoon with a single wastewater treatmentzone for 10 days, the AL will provide approximately 80% BOD removal,i.e., will result in wastewater having 20% of the initial BODconcentration.

Accordingly, the BOD concentration will be reduced from 2,000 mg/L to0.2(2,000 mg/L)=400 mg/L, which is well below the 900 mg/L BODconcentration required for a BOD/N ratio of at least 4/1 and a BOD/Pratio of at least 20/1 in the downstream treatment. This significantlylower effluent BOD concentration will provide very poor C/N andexcessively low C/P ratios for biological nitrogen and phosphorousremoval.

Returning to Example 1, the first wastewater treatment zone achieves FOGand TSS reduction, which is desired upstream of a biological nitrogenand phosphorous removal process while allowing for an adequately highBOD concentration as the organic carbon food source required by thedownstream activated sludge process bacteria to achieve efficientnitrogen and phosphorous removal. The final wastewater treatment zoneeither provides further BOD, FOG, and TSS reduction, or, if required,further wastewater fermentation to break down the wastewater BOD organiccarbon source into short chain volatile fatty acids (SCVFAs), which isthe carbon food source for the bacteria that achieve enhanced biologicalphosphorous removal by luxury uptake in the downstream activated sludgeprocess.

For an anaerobic lagoon treatment system designed and operated toprovide equalized flow at the outlet end, the following applies. If thewastewater influent flow volume is 1,000,000 gallons per day and thefacility is in operation 5 days per week, wastewater is allowed to flowout or is pumped out at a rate of 5,000,000 gallons/7 days=715,000gallons per day or 500 gallons per minute (gpm). Thus, to provide ananaerobic lagoon effluent mixture with a C/N ratio of 4/1 and a C/Pratio of 20/1, the effluent mixture BOD concentration must beapproximately 4× TKN concentration+20× TP concentration. Accordingly,high BOD wastewater must be provided from the first wastewater treatmentzone at an adequate flow rate and mixed with low BOD wastewater from theoutlet end of the final wastewater treatment zone.

As described above, for a wastewater influent having the pollutantconcentrations of Example 1, the BOD concentrations are about 0.7(2,000mg/L)=1,400 mg/L for an effluent from the first wastewater treatmentzone and 0.2(2,000 mg/L)=400 mg/L for an effluent from the secondwastewater treatment zone. Accordingly, mixing the effluents from thefirst wastewater treatment zone and the final wastewater treatment zonein equal amounts will result in a mixture having approximately ((1,400mg/L BOD+400 mg/L BOD)/2)=900 mg/L BOD, TKN=140 mg/L, TP=17 mg/L, and,therefore, a C/N ratio of 4/1 and a C/P ratio of 20/1.

EXAMPLE 2

For wastewater having a higher initial BOD concentration of 2,500 mg/Land identical concentrations for TKN=140 mg/L and TP=17 mg/L andanalogous process parameters, the relative amounts of effluent from thefirst wastewater treatment zone and the final wastewater treatment zonehave to be adjusted as follows to maintain a C/N ratio of 4/1 and a C/Pratio of 20/1.

The BOD concentration in the effluent from the first wastewatertreatment zone is reduced to 0.8(2,500 mg/L POD)=2,000 mg/L BOD and theeffluent from the final wastewater treatment zone is reduced to0.2(2,500 mg/L BOD)=500 mg/L BOD. Accordingly, the mixture prepareddownstream of the anaerobic lagoon treatment system requires thefollowing relative amounts of first and final effluents for a 900 mg/LBOD concentration: x(2,000 mg/L)+(1−x)(500 mg/L)=900 mg/L→x=4/15≈0.267.

Thus, approximately 26.7% of the total effluent flow volume must betaken from the first wastewater treatment zone and 100%−26.7%=73.3% mustbe taken from the final wastewater treatment zone. Further, for a totalequalized flow rate of 500 gpm, a flow rate of 0.267(500 gpm)=133.5 gpmfor the first effluent and a flow rate of 0.733(500 gpm)=366.5 gpm ofthe final effluent should be chosen.

The BOD concentrations and percentages of volume of the effluentsdownstream of the anaerobic lagoon system for the Examples in accordancewith the disclosure and comparative Examples are summarized in Table 1below.

TABLE 1 First BOD Final BOD Effluent concentration concentration volume[mg/L] [mg/L] [%] Example 1 1,400 400 50/50 Example 2 2,000 50026.7/73.3 Comparative n/a 400 —/100 Example

Table 1 shows the BOD concentrations of an effluent from the firstwastewater treatment zone (First BOD concentration) and of an effluentfrom the final wastewater treatment zone (Final BOD concentration) alongwith the relative volumes required to maintain the predetermined ratioof 900 mg/L of BOD by mixing the two effluents. Further, Table 1 shows,where applicable, the corresponding values of the Comparative Example.

The embodiments described hereinabove are further intended to explainbest modes known of practicing it and to enable others skilled in theart to utilize the disclosure in such, or other, embodiments and withthe various modifications required by the particular applications oruses. Accordingly, the description is not intended to limit it to theform disclosed herein. Also, it is intended that the appended claims beconstrued to include alternative embodiments.

The foregoing description of the disclosure illustrates and describesthe present disclosure. Additionally, the disclosure shows and describesonly the preferred embodiments but, as mentioned above, it is to beunderstood that the disclosure is capable of use in various othercombinations, modifications, and environments and is capable of changesor modifications within the scope of the concept as expressed herein,commensurate with the above teachings and/or the skill or knowledge ofthe relevant art.

The term “comprising” (and its grammatical variations) as used herein isused in the inclusive sense of “having” or “including” and not in theexclusive sense of “consisting only of.” The terms “a” and “the” as usedherein are understood to encompass the plural as well as the singular.

All publications, patents and patent applications cited in thisspecification are herein incorporated by reference, and for any and allpurpose, as if each individual publication, patent or patent applicationwere specifically and individually indicated to be incorporated byreference. In the case of inconsistencies, the present disclosure willprevail.

What is claimed is:
 1. An anaerobic lagoon wastewater treatment systemcomprising: an anaerobic lagoon or a tank; a partitioning elementpositioned within the anaerobic lagoon or the tank to define a pluralityof wastewater treatment zones; and a first effluent pipeline fortransporting an effluent from a first wastewater treatment zone fromamong the plurality of wastewater treatment zones to an outlet end ofthe anaerobic lagoon or an outlet end of the tank.
 2. The wastewatertreatment system according to claim 1, wherein wastewater enters thefirst wastewater treatment zone through a wastewater intake port and aneffluent exits a final wastewater treatment zone through an anaerobiclagoon outlet or a tank outlet.
 3. The wastewater treatment systemaccording to claim 2, wherein the first wastewater treatment zone has asmaller volume than the final wastewater treatment zone.
 4. Thewastewater treatment system according to claim 1, wherein thepartitioning element has a plurality of flow holes in a vicinity of alagoon bottom or a tank bottom so that a liquid level is substantiallythe same on both sides of the partitioning element.
 5. The wastewatertreatment system according to claim 1, further comprising a biogascontainment cover.
 6. The wastewater treatment system according to claim5, further comprising a biogas collection system.
 7. The wastewatertreatment system according to claim 1, further comprising onepartitioning element defining the first wastewater treatment zone andthe final wastewater treatment zone.
 8. The wastewater treatment systemaccording to claim 1, further comprising two partitioning elementsdefining the first wastewater treatment zone, a second wastewatertreatment zone, and the final wastewater treatment zone.
 9. Thewastewater treatment system according to claim 8, further comprising asecond effluent pipeline for transporting an effluent from the secondwastewater treatment zone to the outlet end of the anaerobic lagoon orthe outlet end of the tank.
 10. The wastewater treatment systemaccording to claim 1, wherein the partitioning element is selected fromthe group consisting of a concrete wall, a floating cable-mountedmembrane, and a fixed cable-mounted membrane.
 11. The wastewatertreatment system according to claim 1, wherein the partitioning elementis movable to adjust a volume of an adjacent wastewater treatment zone.12. An anaerobic lagoon wastewater treatment system comprising: aplurality of anaerobic lagoons; a first pipeline for connecting a firstanaerobic lagoon to a final anaerobic lagoon from among the plurality ofanaerobic lagoons; and a second pipeline to transporting an effluentfrom the first anaerobic lagoon to an outlet end of the final anaerobiclagoon.
 13. The wastewater treatment system according to claim 12,wherein the first anaerobic lagoon has a smaller volume than the finalanaerobic lagoon.
 14. The wastewater treatment system according to claim12, further comprising a biogas containment cover.
 15. The wastewatertreatment system according to claim 13, further comprising a biogascollection system.
 16. A method of controlling an effluent carbon (BOD)to nitrogen ratio and/or effluent carbon (BOD) to phosphorous ratio ofan anaerobic lagoon wastewater treatment system, comprising: providingan anaerobic lagoon having a plurality of wastewater treatment zones ora tank having the plurality of wastewater treatment zones; reducing aninitial biological oxygen demand (BOD) concentration to a first BODconcentration in the first wastewater treatment zone from among theplurality of wastewater treatment zones; reducing the first BODconcentration or an intermediate BOD concentration to a final BODconcentration in a final wastewater treatment zone from among theplurality of wastewater treatment zones; wherein a difference inconcentration between the initial BOD concentration and the first BODconcentration is smaller than the difference in concentration betweenthe first BOD concentration and the final BOD concentration or betweenthe intermediate BOD concentration and the final BOD concentration; andmixing a first effluent from the first wastewater treatment zone with asecond effluent from the final wastewater treatment zone and/orconducting the first effluent into the final wastewater treatment zone,or conducting the first effluent directly to a downstream activatedsludge denitrification reactor in a nitrification-denitrificationbiological nitrogen and phosphorous removal system.
 17. The methodaccording to claim 16, further comprising: adjusting an amount of thefirst effluent relative to the second effluent to maintain apredetermined ratio of effluent carbon to nitrogen and/or downstream.18. The method according to claim 16, further comprising: providing afirst wastewater detention time for the first wastewater treatment zoneand a final wastewater detention time for the final wastewater treatmentzone, wherein the final wastewater detention time is about four to tentimes longer than the first wastewater detention time.
 19. The methodaccording to claim 18, wherein the first wastewater detention time isabout twelve hours to two days and the final wastewater detention timeis about two days to twenty days.
 20. The method according to claim 18,wherein a first volume of the first wastewater treatment zone is of from10 to 20% of the total volume of the plurality of wastewater treatmentzones and a second volume of the second wastewater treatment zone is offrom 10 to 20% of the total volume of the plurality of wastewatertreatment zones.
 21. The method according to claim 17, furthercomprising: reducing the BOD concentration of the wastewater in thefirst wastewater treatment zone by about 20% to 30%.
 22. The methodaccording to claim 18, wherein the predetermined ratio of effluentcarbon to nitrogen is at least 4:1.
 23. The method according to claim17, wherein a ratio of effluent carbon to phosphorus in the mixture ofthe first effluent and the second effluent is at least 20:1.